If you test too early, before the hormone has had chance to build up enough, you are likely to get a negative even if you are pregnant. GIve it a few more days to a week and test again. By now the levels will have built up if you are pregnant and you should get a positive reading. Its usually best to test on the day you missed your period or after. I wouldve thought it would be present througout the whole pregnancy. When I first tested when I was having my daughter I was actually nearly 4 months gone and it was still present then.